Field of the Invention
This invention relates to a method and an apparatus for converting a 2D (two dimensional) image signal into a 3D (three-dimensional) image signal. In addition, this invention relates to a computer program for converting a 2D image signal into a 3D image signal.
Description of the Related Art
In recent years, movies and broadcasts with 3D video contents have been spread. To allow a viewer to have stereoscopic vision (3D vision), it is necessary to provide a pair of an image for viewer's right eye and an image for viewer's left eye between which a parallax or a disparity is present. Such a pair is referred to as a 3D pair, a 3D image pair, or a stereoscopic image pair also.
In a typical 3D display system with 3D glasses, images for viewer's right eye and images for viewer's left eye are alternately indicated on a time sharing basis, and a viewer wears shutter glasses designed to allow viewer's right eye to observe the indicated right-eye images only and allow viewer's left eye to observe the indicated left-eye images only. The shutter glasses are 3D glasses for enabling the viewer to have stereoscopic vision.
In another typical 3D display system with 3D glasses, images for viewer's right eye are indicated with a first polarization state and images for viewer's left eye are indicated with a second polarization state different from the first polarization state, and a viewer wears polarized glasses designed to allow viewer's right eye to observe the indicated right-eye images only and allow viewer's left eye to observe the indicated left-eye images only. The polarized glasses are 3D glasses for enabling the viewer to have stereoscopic vision.
A conventional glassless 3D display system is designed so that images for viewer's right eye and images for viewer's left eye are indicated on a spatially separation basis, and a viewer does not need to wear 3D glasses. In the glassless system, the resolution of 3D images perceived by the viewer is relatively low.
The typical systems with the 3D glasses and the glassless system are similar in that images for viewer's right eye and images for viewer's left eye are necessary.
Regarding generation of 3D video, there are first and second conventional methods of making 3D image pairs, that is, pairs each having an image for viewer's right eye and an image for viewer's left eye. The first conventional method uses two spatially-separated cameras which simultaneously take a right-eye image and a left-eye image respectively at every shooting moment. The second conventional method uses one camera only. In the second conventional method, every image taken by the camera is edited into an image having a parallax or a disparity relative to the original image. The editing-result image is assigned to one of viewer's right and left eyes while the original image is assigned to the other. Accordingly, the original image and the editing-result image make a 3D pair. Generally, the second conventional method includes a technique of converting a 2D image signal (an output signal from a camera) into a 3D image signal that represents a stream of 3D pairs each having a right-eye image and a left-eye image.
As disclosed in, for example, Japanese patent application publication number 2009-044722, it is known to shift an original 2D image in units of a pixel or pixels through the use of a depth map to generate another 2D image seen from a viewpoint different from that concerning the original 2D image. The shift-result 2D image is assigned to one of viewer's right and left eyes while the original 2D image is assigned to the other. Accordingly, the original 2D image and the shift-result 2D image make a 3D pair. The pixel shift causes lost or missing pixels in the shift-result 2D image. Generally, each of the missing pixels is interpolated from nearby pixels.
An amount of pixel shift is designed to increase as a related step-like depth change is greater. Thus, in the case where a step-like change in depth is great at a boundary between objects in the original image, the number of missing pixels, that is, the missing area in the shift-result image is great at the boundary. As previously mentioned, the missing pixels are interpolated from nearby pixels. When the missing area is large, more places tend to occur where interpolated pixels do not match the positions of corresponding missing pixels. These places deteriorate the shift-result image.